The Woman in Black star revealed how he was able to keep the problem secret despite being a worldwide celebrity. "People with problems like that are very adept at hiding it. It was bad. I don't want to go into details but I drank a lot and it was daily - I mean nightly. I can honestly say I never drank at work on Harry Potter. I went into work still drunk, but I never drank at work."

Radcliffe said that even now he can look back at the movie and pinpoint certain scenes when he worked completely intoxicated. "I can point to many scenes where I'm just gone. Dead behind the eyes."

The star -- who cited his previous alcohol problems in an interview with British GQ last year - said he is now sober and committed to staying that way. "You either have to change something or give into that shame and I wasn’t prepared to do that at 21."